Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $60.66   13.270%   $68.7096   $68.71   $68.70   $68.70  
  Purchase #2 $33.77   6.320%   $35.9043   $35.90   $35.90   $35.90  
  Purchase #3 $109.84   13.335%   $124.4872   $124.49   $124.50   $124.50  
  Purchase #4 $190.78   10.677%   $211.1496   $211.15   $211.15   $211.10  
  Purchase #5 $59.90   11.343%   $66.6945   $66.69   $66.70   $66.70  
  Purchase #6 $201.60   8.341%   $218.4155   $218.42   $218.40   $218.40  
  Purchase #7 $182.93   7.522%   $196.69   $196.69   $196.70   $196.70  
  7 purchase totals = $839.48       $922.0507   $922.05   $922.05   $922.00